Electric switch-board



2 Sheets-Sheet 1.'y

(No Model.)

W. J. MGBLROY. EVLEUTRIG SWITCH BOARD.-

Patented May 29,1883.

llll L l x L (No Model.) Z'Sheets-Sheet 2.

W. J. MOBLROY. ELEGTRIG SWITCH BOARD.

' wah-7 UNITED STATES WILLIAM J. MCELROY, OF PITTSBURG, PENNSYLVANIA.

ELECTRIC SWITCH-BOARD.

SPECIFICATION forming part of Letters Patent No. 273,353, dated May 29,1833.

Application filed February 5, 1883. (No model.)

To all whom it may concern Be it known that I, WILLIAM J. MCELROY, ofPittsburg, county of Allegheny, State of Pennsylvania, have invented ordiscovered a newandusefulmprovementinSwitch-Boards; and I do herebydeclare the following to be a -full,clear, concise, and exactdescription thereof, reference being had to the accompanying drawings,making a part ot this specification, in whichlike letters indicatinglike parts- Figure 1, Sheet Il, is a view in elevation of my improvedswitch-board. Figs. 2, 3, and 4 are views in elevation, to an enlargedscale, of plugs adapted for use in making switch or circuitconnection-011 the board. Figs. 5 and 6, Sheet 2, are views in side andedge elevation of the induction-screen employed in the board. Fig. 7 isan edge vieW, partly broken away, of the switchboard; and Fig. Sis aplan view of one corner of the board, a portion of the platesconstituting the frame being broken away.

Myinvention relates to certain improvementsin switch-boards; and, ingeneral terms, it consists ot' certain combinations of an open frame, ofconducting-bars secured by their ends across the centralopening in theframe, and metal induction-plates between and separate from the bars,with means for securing the plates and bars and for making connectionbetween different bars, as hereinafter more fully described and claimed.

In the useof switch-boards as ordinarily constructed, interferencearises or exists to a considerable degree from two differentsourcesnamely, conduction, sometimes called leakage77 or escape from oneconductor to another throughb the body or substance ot' the board, andinduction, due to the presence of one conductor wit-hin the field orlines of force of another electrically excited. The interference due tothese causes is especially troublesome in telephone service owing toexceeding sensitiveness of these instruments to electric impulse.

rlhe purpose of my invention is to provide a switch-board so constructedas to be free or practically free from disturbance due to these causes,thereby adapting it especially for use on telephone-lines, though itmaybe used with equally good results for ordinary telegraphic purposes.

In the drawings l have represented an open rectangular frame, A, thebars or sides of which are made up ot' three layers of plates, au' a2,

fastened together by screws a3 in any desired number, whereby the partsor plates of the frame may be separated'and replaced at pleasure. Thebars of the frame may be secured together at the angles bylap-joints, orby tenori and mortise, or in any other convenient way. The material ofthe frame is by preference hard rubber or vulcanite, though otherInaterial which is anon'conductor of electricity may be employed.

The conducting=bars c e are passed across the frame from side to side,one set, e, being horizontal, and the other set, o, being vertical. Thebars of each set are separated from each other a sufficient space topermit of the insertion between themvof a plug, R, or S, (shown in Figs.2, 3, and 4, enlarged or full size,) and also the separate sets of barsare separatedin depth suflicient to prevent conduction of elec tricityfrom bar to bar through atmosphere under usual conditions of moistureand pressure. This separation in depth I have shown about equal toone-'third the full thickness ot' the frame-say the full thickness ofthe middle plate, a'. to the frame theirends are passed intoits sides,say, one-halt' their width (more or less) or suiiciently to give a firmksupport. (See Figs. 7 and 8, also dotted lines, Fig. I.) In doing thisrecesses t', ot proper size and form to receive the ends of the front orvertical bars, c, are made in `the inner face of the front or faceplate, a, (see Fig. 7,) and similar recesses, fi', are made for the endsof the horizontal bars c in the inner face of the back plate, a2. (SeeFig. 8.) In order to make electrical connection with the bars, one endis looped, as at c c', forming eyes, through which are passed thefastening bolts or screws u ot` binding-posts N, and to secure certainmetallic contact the barrel n of these posts is letinto the plates oftheframe, (see Fig. 7,) so that the inner shoulder, n, presses firmly uponthe side face ofthe eye. Instead of screw bolts n, equivalent wood'screws or gimlet-pointed screws may be formed yon the end of the barreland screwed into the plate or plates below the eye. I prefer the bolts,however, as affording greater security' and assistance in holding theplates of the frame together. The bars maybe either rect- (See Fig. 7.)In securing the bars` IOO angular in section, as represented in Fig. l,or round, as in Figs. 7 and 8. I prefer the former on account ofaffording increased surface-contact with the switch-plu gs presentlydescribed. They. are, by preference,made of steelor other good electricconducting metal or alloy capable of being hardened by tempering, so asto possess elasticity or spring action sufficient to prevent permanentbending or distortion of the bars. Bars of soft or untempered metal maybe used, however, if made of sufficient size or area in section toretain a straight form under the conditions of use. In this constructionof the frame and bars there is no solid connecting substance between thebars of any kind, except at their ends, air only being in contact withthem over the greater part of their surface. Consequently conductionbetween wires will be limited to such end contact and be reducedpractically to minimum or nothing. In this respect decided advantage isgained over boards employing a body or back in contact with the whole orgreater part ofthe length of the switeh-bars, as commonly practiced.Itis well known that air is among the best of insulators, and byproviding` for air-contact along with the whole surface ofthe bars,except their ends, I secure to a corresponding extent the greatestattainable degree of insulation, and consequent protection againstconduction or escape of electric force from wire to wire. In

l order to make the desired electric connection between the bars ot' thetwo sets, I make use of a plug, R, Fig. 2, having a head, 9, of hardrubber or other suitable non-conductor, and a fourpronged metal body,r', the space r2 between prongs corresponding in width to the thicknessofthe bars, so that the prongs may straddle the bars at thecrossing-points, with their fiat inner faces pressing closely upon theflat side faces of the bars. Other than ilat faces may be used, eitheron the hars or prongs, or both, and still secure electrical contact orconnection. I prefer the fiat forms, however, on account of theincreased contactsurfaee secured thereby.

In Figs. 3 and 4 I have shown a modified form of plug, S, moreespecially adapted to straddle around bars, as in Figs 7 and 8,consisting of non-conducting head s, short and long prongs s s2, forminga hook for engaging a portion ot' the surface of the front bar, thelonger prong, s?, beingsplit, as at s, and having a seat or recess, s,in such split, at or near the point adapted to receive the rear bar, thetwo parts of the split prong separating to receive the bar, and thenpressing it with spring action to insure good contact. In this form ofplug the distance between the seats should correspond accurately withthe distance between bars, so as to press them firmly. This calls foraccuracy of fitting, and for this reason, as well as for its adaptationto the pre ferred form of bars, Fig. 1, I prefer the form of plug shownin Fic". 2. Both, however, em-

brace substantially the saine features of fourpronged construction, theshort and long prongs s s forming two for the front bar, and the splitin prong s2 forming, in effect, two prongs for the rear bar. I thereforeconsider both these forms as coming within my invention, in the sense ofbeing four-pronged, and adapted to embrace two sides of the bars andthereby obtain the requisite support and im! part the desiredpressurecontact.

` In providing against conduction of electric force in the constructionofthe board, as above described, one material and important source ofinterference is practically removed.

In order to provide against induction, two sets or series of plates orbars, d b, are einployed, one set, as b, being arranged parallel withand midway between thefront bars, c, or between pairs of such bars, andthe other set, d, being arranged in like manner between the rear bars,c. These plates b d are made of some soft conducting metal, bypreference soft iron, and may be nickel-plated or otherwise coated toprevent oxidation. Also, if desired, the bars c c may be protected inlike manner.

As represented in Figs. 5 and G, the plates b cl are arranged acrosseach other, edge to edge, and they may be rigidly secured together insuch relationship by screw-bolts or by soldering, or in other convenientway, forming what Iterin an induction-screen,77 I3, which is supportedin position within the opening in the main frame A by corner-stays h onthe back, secured by screws or in other convenient way. The combinedwidth of bars b d is, by preference, about equal to the thickness offrame A, bringing their outer-edge faces and the side faces of the framein or near the saine planes. As before described, the two sets of bars ce are let into the inner faces ofthe outer pieces ,a aofthefraine.Consequently each set of such bars will be nearly in central plane oftheir respective sets of induction-plates Z; d, as represented in Fig.7, so that thelatter will extend in depth both in front and rear of theplane of the conducting-bars. rJhus the induction-plates, so far as theyextend, intercept all lines of force between conducting-bars, and ifmade ot' appreciable body or thickness-say about equal to the thicknessot' the conductingbars-they will arrest the force exerted in such lines,thereby protecting or shielding the conducting-bars. Also, by making theinductionplates to overreach or exceed the conductors in depth,bothforward and backward,they cover or subtend a greater arc ofradiation than the conductors,andwill shield them not only from directradial lines of force, but also from diffusion of force, the conductorslying, as it were, withina deep shadowin the field efforce, which shadowis formed or projected by the overreaching induction-plates. Byprojecting the conductors in this manner induction will be so farreduced as to give :no trouble and for all practical purposes to beabsent. The ends of the conductors alone are unprotected, and theexposure thus made is so small as to produce IOO ICIS

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no troublesome interference. It' desired, the induction-plates may becarried closer to the inner edge of the frame than shown, or they may bepassed into the frame, say, the full depth of the conducting-bars. Iprefer, however, to stop them a little short of the frame,

as shown, in order better -to prevent conduc tion.

If desired, the induction-screen may have ground connection of anysuitable kind to carry oi' any electric currents that may be excitedtherein by reason of its position in the eld of force of theelectrically-excited conductors.

I have shown the bars c ein each set grouped in pairs, forming loops forincoming and outgoing lines, and the induction-plates b d placed betweensuccessive pairs instead of between individual successivebars. ,Thisform of board is designed more especially' for wayoftices. For aterminal office all the bars would be separated by suchinduction-plates, as each bar might form part `of a separate line. Inboth cases the bars forming parts of separate lines are separated byintermediate induction-plates. Theforces which cause the interferencesabove described are, relatively speaking, small but dit'ticult tocontrol, and capable of causing serious trouble, especially intelephonie service.

The -features of improvementI herein described by which such troublesare materially reduced .or practically removed are, therefore, of greatutility and advantage.

1 claim herein as my invention- 1. In a switch-board', the combinationof two sets ot conducting-bars crossing the board in different planesand directions for line-connec tions, with induction -plates of metalinterposed between the conducting-bars in each set, substantially as andfor the purposes set forth.

2. In a switch -board, the combination of frame A, with open interior,two sets of conducting-bars, c e, crossing the open space within theframe in different planes and directions, and induction-plates b d,interposed between the conducting-bars in each set, the conductors andplates being unconnected within the frame by solid substance,substantially as set forth.-

8. The combination ot' frame A, conductingbars c e, crossing the openspace in the frame in diierent planes and directions, andinduction-plates b d, interposed between the conducting-bars, andoverreaching -the bars in depth, both in front and rear, substantiallyas and for the purposes set forth.

4. Theinduction-screen B, composed of metal plates b cl in di'erentplanes, crossing each other edge to edge, in combination withconducting-bars c e, interposed between the plates in or near theircentral planes and surrounding frame A, substantially as set forth.

5. A switchboard having a frame with open inner space andconducting-bars crossing such open space .in different planes anddirections, in combination with a switch-plug havin g separate prongsadapted to straddle the conducting-bars and press their side faces,substantially as and for the purposes set forth.

6. A switch-plug having a non-conducting `head and a four-prongedmetallicbody, substantially as and for the purposes set forth.

In testimony whereof I have hereunto set my hand.

WILLIAM J. MGELROY.

Witnesses:

R. H. WHITTLESEY, C. L. PARKER.

